DE102004033475A1 - Corrosion protection for micromechanical sensor elements, e.g. for a pressure sensor, comprises a passivating agent that at least partially covers electrical components and a material layer applied to the top of the passivator - Google Patents

Abstract

Device, especially a pressure sensor, has a housing (250), at least an electrical component (110, 120, 130) and is at least partially filled with a passivating agent (140) so that the electrical component is at least partially covered by the passivating agent. An additional material layer (200) is applied in or on the passivating agent. The additional area prevents formation of a free space above the passivating agent in which corrosion inducing chemicals or compounds could collect. The invention also relates to a method for producing an inventive device.

Description

The The invention is based on a micromechanical pressure sensor or of a method for manufacturing a micromechanical pressure sensor wherein a sensor element in a housing with a Passivierungsmittel is covered.

To the Protecting a sensor from damaging environmental influences can the sensor element with a special passivation layer to be covered. This happens, for example, such that the sensor element or the (electrical and / or mechanical) components used for Detection and / or evaluation of a sensor signal are required, in a housing be mounted and then covered with a passivating agent. Usually, this passivation is by a backfilling of the housing reached. The backfilling serves the passivation of the sensor element or the protection the components opposite Media such as water, air, gasoline, salt, etc. Thus, corrosion can occur sensitive elements of the sensor can be prevented. Problematic in passivation, however, is the interaction of the passivating agent with the injurious Medium.

Micromechanical Pressure sensors in which the system-pressure of the sensor chip front side supplied Usually, a gel such as one is used Fluorosilicone gel before environmental influences protected. This gel covers the surface of the chip or the bonding wires and Prevents corrosive media from coming in contact with the chip can. However, when choosing the gel, make sure that the gel the pressure of the medium to detect a print size on the Pressure sensor membrane in the sensor chip transmits.

For the application of pressure sensors in a highly corrosive environment, as regularly in the exhaust system A vehicle engine can be observed even the best currently available gels Do not prevent corrosive components of the medium over time diffuse through the gel and cause corrosion of the sensor element or other components on the sensor chip.

A expensive construction variant to protect the pressure sensor, is that the Sensor element consisting of sensor chip and bonding wires in one with silicone oil filled Chamber is mounted over a steel membrane keeps in contact with the environment. A change in ambient pressure will over the steel membrane directly to the silicone oil and thus to the sensor element or forwarded the sensor chip.

Advantages of invention

The The present invention describes a device with a housing and at least one electrical component, wherein the housing at least having one of the electrical components and at least partially filled with a passivating agent. Furthermore, it is envisaged that the electrical component at least partially with the passivating agent is covered. The core of the invention is now that on the passivating agent an additional Material layer is applied. With this additional material layer can a simpler and cheaper Building one opposite environmental damage resistive device can be realized. Thus, the use becomes of electrical components in corrosive environments.

In A particular embodiment of the invention is provided that the electrical component a particular micromechanical sensor element having. In this case, the micromechanical sensor element both a Print size, one temperature size, one Air mass, a resistance and / or detect a concentration of at least one medium. conveniently, A medium surrounds at least a part of the device and / or the micromechanical sensor element.

Especially It is advantageous that by the choice of the passivating agent in combination with the material of the additional material layer an optimized Seal of the electrical component or the sensor element is reached. Thus, damage to the sensor element by corrosive Media be prevented. About that In addition, by the structure according to the invention also the use of the pressure sensor in liquid Media possible, because the material of the additional Material layer selected such that can be that liquid Medium is separated from the passivating agent.

Furthermore is provided that the electrical component, in particular the Sensor element, having corrosion-sensitive areas. This can be, for example Contact surfaces or be elements such as bonding pads and / or bonding wires. advantageously, are therefore at least these corrosion-sensitive areas with covered by the passivating agent.

In a particular embodiment of the invention, the surrounding medium is separated from the passivating agent by the additional material layer. Advantageously, however, can also be provided that the additional material layer through a corresponding chemical reaction renders harmless the corrosive components of the ambient medium that would otherwise attack the electrical components. Another way to increase the life of the electronic components and thus the service life of the sensor is to reduce by means of suitable materials, the diffusion rate of the corrosive components of the surrounding medium. Particularly advantageous is the use of corrosion-resistant and / or water-impermeable materials in the additional material layer.

Preferably is the extra Material layer formed as a membrane layer, wherein provided may be that the membrane layer has a wavy surface texture having. This wavy surface structure can compensate for a temperature-induced expansion of the passivation agent, without causing a crack in the membrane layer.

In a development of the invention is as Passivierungsmittel fluorosilicone gel and / or as additional Material layer is a layer of a corrosion-resistant and / or water-impermeable material such as Teflon or a parylene provided. Farther is provided in a particular embodiment of the invention, that the passivating agent and the material of the additional Material layer matched temperature expansion coefficient exhibit.

It is provided that the housing, in which the sensor element is mounted, a lower housing part having housing walls. In this case, advantageously, the lower housing part to the height of the housing walls with filled the passivation agent.

Furthermore is provided in a further embodiment of the invention that the housing an upper housing part having a housing cover. This housing cover is preferably mounted on the housing so that he additional Material layer fixed on the passivating agent. It can be provided that the housing cover only after applying the additional Material layer is placed on the passivation agent. It However, it is also conceivable that the additional material layer directly in the housing cover is introduced and only after placing the housing cover on the lower housing part covers the passivating agent.

Around a forwarding of the pressure change of To allow media to the sensor element is in the housing cover an opening provided by which the medium in contact with the additional material layer can occur.

advantageously, is provided, the electrical contacting surface and / or the electrical contacting element with at least one predefinable layer thickness of the passivating agent to cover. Thus, for example, be provided over at least a bonding pad and / or a bonding wire, the passivation agent in a thickness of at least 0.2 mm apply. By such a predefinable layer thickness of the passivating agent can be achieved that the corrosion causing Components of the medium are not or delayed to the corrosion-sensitive Reach areas.

A Possibility, the speed with which the medium or components of the medium to penetrate into the passivating agent is to reduce as additional Material layer of platelet-shaped fillers such as. mica flakes into the passivating agent. But it is also wrong the addition of platelet-shaped fillers such as hydrotalcite, magnesium hydroxide, aluminum hydroxide, hydromagnesite or huntite in the passivating agent conceivable to the diffusion rate reduce or increase the diffusion path.

Besides However, it may also be provided that the corrosive components of Medium, which can diffuse into the passivating, by a suitable chemical reaction (neutralization or adsorption) harmless close. For example, amino-functionalized siloxanes can be used as a material of the additional Material layer in which the aminopropyl groups as bases with corrosive acids react under salt binding. acids can also by mono-, di- or trialkylamines, silicanes or amino-terminated silicone oil or acid-binding fillers such as hydrotalcite, magnesium hydroxide, aluminum hydroxide, hydromagnesite be bound.

Generally it can be provided that the device has a particular micromechanical pressure sensor for detecting a pressure of an ambient medium representing Represents print size. About that However, it is also conceivable that the device is a relative Print size of two media detected. Due to the inventive design is the use of such a pressure sensor in the exhaust stream or possible in the tank of a motor vehicle. About that However, it is also conceivable that the device has a (hot) Air mass sensor or a generator control device represents.

By a suitable choice of the passivation agent or the materials for the additional material layer, it is also possible to reduce the shaking load of reimbursed bonding wires. For example, an inflexible barrier can reduce gel displacement amplitudes of the passivation gel.

at the use of the seal according to the invention of the passivating agent is a saving of hermetic or splash-proof housings possible, to protect the gel rooms be used in electrical and / or electronic components. Furthermore, by such a seal also the use of oil-sweating gels considered in electronic components who are not in contact with volatile, bleeding ingredients of a passivation gel.

Further Benefits emerge from the following description of exemplary embodiments or from the dependent ones Claims.

drawings

1 shows a micromechanical pressure sensor in a housing, as is known in the prior art. 2 shows a first embodiment of the invention, whereas 3 shows a second embodiment of the invention.

embodiment

In 1 a known structure of a micromechanical pressure sensor is shown in a housing. In this case, a preferably micromechanical sensor element, for example from a substrate 110 and a sensor chip 120 on a support element 100 applied. In general, however, it should be assumed that the sensor element can also be realized by a different structure. Common materials for the micromechanical sensor element are semiconductor materials or steels. As a carrier element 100 For example, ceramics or printed circuit boards are used. The sensor chip 120 For example, with a membrane 190 and a cavern having a predetermined pressure 180 be equipped. However, it can also be provided that the substrate 110 and the carrier element 100 for differential pressure applications a passage to the membrane 190 having. Between the pressure in the cavern 180 and the ambient pressure of the sensor is a pressure difference. A variation of the ambient pressure manifests itself in a movement of the membrane 190 , By suitable electrical components such as piezoelectric resistors (not shown) on the membrane 190 This movement can be converted into a measured variable, which is generated in proportion to the pressure difference occurring. To forward this parameter are connecting elements such as bonding wires 130 provided by the sensor chip 120 for further evaluation of the measured variable, for example, on the carrier element 100 be guided. Usually, these bonding wires 130 using bonding pads on the sensor chip 120 and / or the carrier element 100 attached. However, it is also conceivable that on the sensor chip 120 and / or on the carrier element 100 Contact surfaces are provided, via which a control of the sensor chip 120 and / or an evaluation or forwarding of the measured variable. To protect the sensor element from damage, the sensor element is housed in a housing. The case can be as in 1 shown, both only of housing walls 150 as well as from housing walls 150 including a housing cover 155 consist. So that the sensor element or the membrane 190 can detect the pressure difference to the environment, it is provided that the housing cover 155 an opening 170 through which the medium on the membrane 190 can work. Since the contacting points of the bonding wires and / or the further electrical components of the sensor element are corrosion-sensitive areas, it is provided that the interior of the housing 150 respectively. 155 with a passivating agent 140 for example, to replenish a gel. When choosing the passivating agent 140 Care must be taken to ensure that all corrosion-sensitive areas are adequately covered, so that they are protected from the possibly corrosive medium. In addition, this is the passivating agent 140 to choose such that it is so soft on the one hand, that there is no mechanical tension on the sensor membrane 190 on the other hand, however, the ambient air pressure in the direction 160 acts directly on the membrane 190 forwards.

In highly corrosive environments, such as in the exhaust system of an internal combustion engine, even the best passivation gel currently available can not adequately protect the pressure sensor chip from corrosion. Therefore, in addition to the passivating gel, another layer of material is applied directly to the gel, as shown in Figs 2 and 3 is shown.

In 2 the housing of a pressure sensor is shown, which only by a housing walls 250 is realized. As already in 1 shown, the sensor element and the bonding wires 130 with a passivating agent 140 covered. Advantageously, it is provided that all elements of both the sensor element and the connecting elements are completely covered, which is not a necessity. Only the coverage of the corrosion-sensitive areas is a necessary measure. Advantageously, a minimum thickness of the covering is provided to ensure adequate protection of the corrosion-sensitive areas from the corrosive components of the ambient medium. So in the case 250 introduced passivating agent 140 then becomes an additional layer of material 200 applied, preferably the entire surface of the passivating agent 140 covered. This can be done for example in the form of a membrane. With such a covering of the passivating agent 140 prevents the medium from being in contact with the passivating agent 140 comes. When choosing the material of the additional material layer 200 Make sure that the layer 200 is sufficiently flexible to pass the ambient pressure directly to the gel. For this reason, it is also advantageous if there is no longer any air between the gel and membrane, since otherwise the trapped air could expand with temperature increases and could lead to an unwanted and disturbing pressure signal. Furthermore, the material of the layer should 200 be chosen so that it does not pass through corrosive media but also no water, the membrane itself the media and a temperature-induced expansion of the passivating agent 140 must withstand. By appropriate surface structuring of the layer 200 , For example, by a wave pattern, is also a compensation of the temperature-induced expansion of the passivation 140 possible.

As a possible material for the layer 200 offers Teflon due to its favorable properties. Furthermore, in a particularly suitable embodiment, the layer 200 be executed from a parylene or contain such. By parylenes is meant substituted or unsubstituted polyparaxylenes or poly [2,2] -paracyclophanes. Suitable substituents are, in particular, halogens such as fluorine, chlorine and bromine, it being possible for the parylenes to be mono-, di-, tri- or tetrasubstituted. The layer 200 is preferably carried out with a layer thickness of 1 to 50 microns.

When Passivating agents are preferably silicone gels, for example based on polydimethylsiloxane (PDMS) or polyphenylmethylsiloxane used or (per) fluorinated silicone gels such as perfluorinated PDMS. Furthermore, gel systems are based on optionally (per) fluorinated polyethers or vinyl polymers, the crosslinkers with hydridic siloxane units, fillers, optionally thixotropic agents, Adhesion promoters, inhibitors and catalysts included, suitable.

Contrary to the illustration in 2 However, it can also be provided that the passivating agent 140 up to the maximum height of the housing walls 250 can be filled. However, it should be noted that the additional layer 200 the entire surface of the passivating agent 140 cover to provide optimum protection or sealing. One way in which such a cover can be achieved is in 3 shown. In this presentation, this is already out of the 1 and 2 known sensor element with the passivating agent 140 down to the height of the housing walls 350 refilled. Subsequently, an additional layer of material is applied to the thus filled housing 300 applied, in addition to the passivating agent 140 also parts of the housing walls 350 covers. The overlap of the cover of the housing walls 350 through the material layer 300 is necessary to prevent edge effects resulting from insufficient coverage of the passivating agent in the range 390 could be generated. Otherwise, these edge effects could in the worst case lead to penetration of the medium into the passivating agent 140 and lead to damage of the sensor element. After applying the layer 300 Optionally available as a lid 355 designed housing top are applied firmly, the layer 300 on the housing base 350 pinched and fixed. If necessary, the lid can 355 with the housing lower part 300 welded or glued. An opening 370 in the lid 355 allows the pressure of the medium in the direction 160 on the membrane 190 to let act.

In a further embodiment, the additional layer 300 directly in the lid 355 placed before the lid on top with the passivating agent 140 filled lower housing part 350 is applied.

Due to the inventive design of the pressure sensor, the sensor is suitable for both gaseous and liquid media. Here offers the additional material layer 200 respectively. 300 a protection that the passivating agent alone can not offer. As a result, for example, surface micromechanically produced pressure sensors can be used in liquid media.

In 4 another embodiment is shown, which is the protection of a sensor element 400 , an evaluation circuit 420 as well as a bond connection 430 shown. Usually, the sensor element becomes 400 with the help of an adhesive or a solder 410 on the carrier element 100 applied. A housing wall 450 or a gel ring allows the filling of the interior or the covering of the sensor element 400 with a corresponding passivating agent 140 , wherein the additional material layer 460 according to 4 directly into the passivating agent 140 can be introduced. There is the possibility that first the passivating agent 450 is replenished before the additional material layer 460 is introduced. This For example, this can be done by applying to the not yet solidified passivation agent 140 a wafer is deposited, which sinks during the curing process. Of course, it can also be provided that the plate only on the surface of the passivating agent 140 is placed and remains there. In addition, there is the possibility of the additional material layer 460 by mixing the additional material into the passivating agent 140 to create. Thus, for example, crosslinking of the introduced materials can be achieved during hardening or a further special treatment of the sensor. However, it is also conceivable that corresponding solvents are used in a diffusion of the material for the additional material layer during the production of the sensor.

The additional material layer 460 the example of 4 may be chosen to prolong the diffusion path of the corrosive constituents of the medium which penetrate into the passivating agent and destroy the corrosion-sensitive areas. This happens because the chosen material reduces the diffusion speed. For such an extension of the diffusion path of the corrosive constituents are platelet-shaped fillers such as mica flakes or materials such as hydrotalcite, magnesium hydroxide, aluminum hydroxide, hydromagnesite or huntite. The magnesium hydroxide is a high-temperature non-toxic flame retardant, which simultaneously acts as an acid binder. The hydrotalcite can be used as a layered, basic magnesium aluminum hydroxy carbonate.

• – Salzsäure,
• – Salptersäure,
• – Schwefelsäure,
• – Carbonsäuren,
• – Alkohole,
• – Aldehyde oder
• – Ammoniak

enthalten. Dabei können die Agenzien sowohl gasförmig oder als Kondensat den Sensor angreifen.Diffusing corrosive agents against which the electrical or electronic components must be protected, for example

• Hydrochloric acid,
• - nitric acid,
• Sulfuric acid,
• - carboxylic acids,
• - alcohols,
• - aldehydes or
• - ammonia

contain. The agents can attack the sensor either in gaseous form or as condensate.

Next the extension the diffusion path can also be provided, the additional Material layer with a material form, which is the corrosive Agents or components of the medium by means of a chemical Reaction harmless. As the electrical and / or electronic components predominantly of acidic Components of the medium to be attacked is in a special embodiment The invention provides the material layer and / or the passivating agent enrich with basic compounds. This is done, for example, by using amino functional siloxanes, the latter being present contained aminopropyl groups with the acid under a salt formation react. Another advantage is that amino-functionalized Siloxanes polymerized in the preparation in the passivating agent can be. One more way consists in the use of highly viscous amino-terminated silicone oil, which also acids as salts binds. A similar Function silicans such as Fluorochem PS 112, a cross-linked Poly (1,1-dimethylsilazane) on.

In addition to the previously listed materials for the additional material layer 200 . 300 respectively. 460 also acetamides such as bis / trimethylsily) acetamide can be used, which can react with alcohols, phenols and acids. A similar effect is achieved with carbamates such as N, O-bis (trimethylsilyl). In addition, however, organic bases such as polyethyleneimine and polyamines are also conceivable as constituents of the additional material layer.

The fillers Hydrotalcite, magnesium hydroxide, aluminum hydroxide. Hydromagnesit are in addition to their diffusion path extending effect as acid binder effective.

Claims (16)

Device with a housing ( 250 . 350 . 355 . 450 ) and at least one electrical component ( 110 . 120 . 130 . 400 . 420 . 430 ), the housing ( 250 . 350 . 355 . 450 ) - at least one of the electrical components ( 110 . 120 . 130 . 400 . 420 . 430 ) and - at least partially with a passivating agent ( 140 ), and wherein the electrical component ( 110 . 120 . 130 . 400 . 420 . 430 ) at least partially with the passivating agent ( 140 ), characterized in that in or on the passivating agent ( 140 ) in the housing ( 250 . 350 . 355 . 401 an additional layer of material ( 200 . 300 . 460 ) is applied. Apparatus according to claim 1, characterized in that the electrical component ( 110 . 120 . 130 . 400 . 420 . 430 ) a micromechanical sensor element ( 110 . 120 . 400 ), wherein it is provided in particular that by means of the micromechanical sensor element ( 110 . 120 . 400 ) - a pressure variable and / or - a temperature variable and / or - an air mass and / or - a resistance variable and / or A concentration of at least one of the device and the micromechanical sensor element ( 110 . 120 . 400 ) surrounding medium is detected. Apparatus according to claim 1, characterized in that the electrical component ( 110 . 120 . 400 ) at least one corrosion-sensitive area, in particular a contacting area or a contacting element such as a bonding pad and / or a bonding wire ( 130 . 430 ), wherein it is provided that this corrosion-sensitive area with the passivating agent ( 140 ) is covered. Device according to claim 1, characterized in that the material layer ( 200 . 300 . 460 ) - the passivating agent ( 140 ) separates from an ambient medium and / or - the diffusion rate of an ambient medium in the passivation agent ( 140 ) and / or - makes harmless a corrosive constituent of an ambient medium by a corresponding chemical reaction, wherein it is provided in particular that the material layer ( 200 . 300 . 460 ) has a corrosion-resistant and / or water-impermeable material. Device according to claim 1, characterized in that the material layer ( 200 . 300 . 460 ) is formed as a membrane layer, wherein it is provided in particular that the membrane layer has a wave-shaped surface structure. Device according to one of claims 1 to 5, characterized in that - the passivating agent ( 140 ) a gel, in particular a fluorosilicone gel, and / or the material of the material layer ( 200 . 300 . 460 ) Teflon or a parylene. Device according to one of claims 1 to 6, characterized in that the passivation agent ( 140 ) and the material of the material layer ( 200 . 300 . 460 ) Have coefficients of thermal expansion which largely correspond. Device according to one of the preceding claims, characterized in that the housing ( 250 . 350 . 355 . 450 ) a housing lower part with housing walls ( 250 . 350 . 450 ), wherein it is provided that the lower housing part up to the height of the housing walls with the Passivierungsmittel ( 140 ) is filled. Device according to one of the preceding claims, characterized in that the housing ( 250 . 350 . 355 ) an upper housing part with a housing cover ( 355 ), wherein it is provided that the housing cover ( 355 ) - an opening ( 370 ) and - the material layer ( 300 ) on the passivating agent ( 140 ) fixed. Apparatus according to claim 3, characterized in that the electrical contacting surface and / or the electrical contacting element with at least one predetermined layer thickness of the passivating agent ( 140 ), wherein it is provided in particular that the passivating agent ( 140 ) via at least one bonding pad and / or a bonding wire ( 130 . 430 ) has a layer thickness of more than 0.2 mm Apparatus according to claim 4, characterized in that the material of the material layer ( 200 . 300 . 460 ), which is suitable for reducing the rate of diffusion of the ambient medium or the diffusion rate of part-substances of the medium in the passivating agent, comprises - at least one mica flake or - as material component - hydrotalcite or - magnesium hydroxide or - aluminum hydroxide or - hydromagnesite / huntite. Apparatus according to claim 4, characterized in that the material of the material layer ( 200 . 300 . 460 ), which is capable of neutralizing corrosive constituents of the medium by a corresponding reaction, at least - amino-functionalized siloxanes or - silicanes or - a high-viscosity amino-terminated silicone oil or - mono-, di- or trialkylamines or - hydrotalcite or - magnesium hydroxide or - aluminum hydroxide or - hydromagnesite / huntite. Device according to one of claims 1 to 12, wherein the device - one Micromechanical pressure sensor for detecting a - the pressure an ambient medium or - the pressure difference of two Representing surrounding media Print size, or - one Hot air mass sensor or - A generator control device represents. Method for producing a device, in particular a device according to one of Claims 1 to 11, having a housing ( 250 . 350 . 355 . 450 ) and at least one electrical component ( 110 . 120 . 130 . 400 . 420 . 430 ), the housing ( 250 . 350 . 355 . 450 ) - at least one of the electrical components ( 110 . 120 . 130 . 400 . 420 . 430 ) and - at least partially with a passivating agent ( 140 ), and wherein the electrical component ( 110 . 120 . 130 . 400 . 420 . 430 ) at least partially with the passivating agent ( 140 ), characterized in that in or on the passivating agent in the housing ( 250 . 350 . 355 . 450 ) an additional layer of material ( 200 . 300 . 460 ) is applied. Method according to claim 14, characterized in that before filling the housing ( 250 . 350 . 355 . 450 ) with the passivating agent ( 140 ) on the electronic component ( 110 . 120 . 400 ) at least one electrical contacting surface and / or an electrical contacting element is produced, wherein it is provided in particular that the contacting surface and / or the contacting element - a bonding pad and / or a bonding wire ( 130 . 430 ) and / or - with the passivation material ( 140 ) is covered. A method according to claim 15, characterized in that the electrical contacting surface and / or the contacting element with at least one predetermined layer thickness of the passivating agent ( 140 ), wherein it is provided in particular that the passivating agent ( 140 ) via at least one bonding pad and / or a bonding wire ( 130 . 430 ) has a layer thickness of more than 0.2 mm.